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Solar Influence on Temperature (Asia) -- Summary
Climate alarmists frequently claim that earth's climate is becoming more variable and extreme as a result of CO2 induced global warming. With respect to temperature, we have shown elsewhere on our website that its modern frequency and severity fall well within the range of natural variability (see Natural Variability of Climate and Temperature Trends in our Subject Index). In the present review, we examine the issue of attribution, specifically investigating the natural role or influence of the sun on temperature in Asia.

We begin with a 2003 paper published in the Russian journal Geomagnetizm i Aeronomiya (Vol. 43, pp. 132-135), where two scientists from the Institute of Solar-Terrestrial Physics of the Siberian Division of the Russian Academy of Sciences challenged the politically-correct global warming dogma that vexes the entire world. The two scientists, Bashkirtsev and Mashnich (2003), say "a number of publications report that the anthropogenic impact on the Earth's climate is an obvious and proven fact," when in actuality, in their opinion, "none of the investigations dealing with the anthropogenic impact on climate convincingly argues for such an impact."

In the way of contrary evidence, they begin by citing the work of Friis-Christensen and Lassen (1991), who first noted the close relationship (r = -0.95) between the length of the sunspot cycle and the surface air temperature of the Northern Hemisphere over the period 1861-1989, where "warming and cooling corresponded to short (~10 yr) and prolonged (~11.5 yr) solar cycles, respectively." They then cite the work of Zherebtsov and Kovalenko (2000), who they say established a high correlation (r = 0.97) between "the average power of the solar activity cycle and the surface air temperature in the Baikal region averaged over the solar cycle." These two findings, they contend, "leave little room for the anthropogenic impact on the Earth's climate." In addition, they note that "solar variations naturally explain global cooling observed in 1950-1970, which cannot be understood from the standpoint of the greenhouse effect, since CO2 was intensely released into the atmosphere in this period," citing in support of this statement the work of Dergachev and Raspopov (2000).

With respect to original work, Bashkirtsev and Mashnich conducted wavelet-spectra and correlation analyses of Irkutsk and world air temperatures and Wolf number data for the period 1882-2000, finding periodicities of 22 (Hale cycle) and 52 (Fritz cycle) years and reporting that "the temperature response of the air lags behind the sunspot cycles by approximately 3 years in Irkutsk and by 2 years over the entire globe."

Noting that one could thus expect the upper envelope of sunspot cycles to reproduce the global temperature trend, they created such a plot and found that such is indeed the case. As they describe their results, "the lowest temperatures in the early 1900s correspond to the lowest solar activity (weak cycle 14), the further temperature rise follows the increase in solar activity; the decrease in solar activity in cycle 20 is accompanied by the temperature fall [from 1950-1970], and the subsequent growth of solar activity in cycles 21 and 22 entails the temperature rise [of the last quarter century]."

With respect to the future, Bashkirtsev and Mashnich say "it has become clear that the current sunspot cycle (cycle 23) is weaker than the preceding cycles (21 and 22)," and that "solar activity during the subsequent cycles (24 and 25) will be, as expected, even lower," noting that "according to Chistyakov (1996, 2000), the minimum of the secular cycle of solar activity will fall on cycle 25 (2021-2026), which will result in the minimum global temperature of the surface air (according to our prediction)." Still, only time will tell if such predictions prove correct.

Turning our attention back to the past, but staying in the Asian subarctic, Vaganov et al. (2000) utilized tree-ring width as a proxy for temperature to examine temperature variations in this region over the past 600 years. According to a graph of their data, temperatures in the Asian subarctic exhibited a small positive trend from the start of the record until about 1750. Thereafter, a severe cooling trend ensued, followed by a 130-year warming trend from about 1820 through 1950, after which temperatures fell once again. In considering the entire record, they further state that the amplitude of 20th-century warming "does not go beyond the limits of reconstructed natural temperature fluctuations in the Holocene subarctic zone."

In attempting to determine the cause or causes of the temperature fluctuations, the researchers report finding a significant correlation with solar radiation and volcanic activity over the entire 600-year period (R = 0.32 for solar radiation, R = -0.41 for volcanic activity), which correlation improved over the shorter interval of the industrial period -- 1800 to 1990 -- (R = 0.68 for solar radiation, R = -0.59 for volcanic activity).

It is interesting to note that in this region of the world, where climate models predict large increases in temperature as a result of the historical rise in the air's CO2 concentration, real-world data show an actual cooling trend since around 1940, when the greenhouse effect of CO2 should have been most prevalent. And, where warming does exist in the record (between about 1820 and 1940), much of it correlates with changes in solar irradiance and volcanic activity - two factors definitely free of anthropogenic influence.

In two additional paleoclimate studies from the continental interior of Russia's Siberia, Kalugin et al. (2005) and Kalugin et al. (2007) analyzed sediment cores from Lake Teletskoye in the Altai Mountains (5142.90'N, 8739.50'E) to produce multi-proxy climate records spanning the past 800 years. Analyses of the multi-proxy records revealed several distinct climatic periods over the past eight centuries. With respect to temperature, the regional climate was relatively warm with high terrestrial productivity from AD 1210 to 1380. Thereafter, temperatures cooled, reaching peak deterioration between 1660 and 1700, which time period, in the words of Kalugin et al. (2005), "corresponds to the age range of the well-known Maunder Minimum (1645-1715)" of solar sunspot activity.

Moving over to Japan, an uninterrupted 1100-year history of March mean temperature at Kyoto was developed by Aono and Kazui (2008), who used phenological data on the times of full-flowering of cherry trees (Prunus jamasakura) acquired from old diaries and chronicles written at Kyoto. Upon calibration with instrumental temperature measurements obtained over the period 1881-2005, the results were compared with the sunspot number history developed by Solanki et al. (2004).

The results of the study suggest "the existence of four cold periods, 1330-1350, 1520-1550, 1670-1700, and 1825-1830, during which periods the estimated March mean temperature was 4-5C, about 3-4C lower than the present normal temperature." The researchers state that "these cold periods coincided with the less extreme periods [of solar activity], known as the Wolf, Spoerer, Maunder, and Dalton minima, in the long-term solar variation cycle, which has a periodicity of 150-250 years." In addition, they report that "a time lag of about 15 years was detected in the climatic temperature response to short-term solar variation."

Also in Japan, Kitagawa and Matsumoto (1995) analyzed δ13C variations of Japanese cedars growing on Yakushima Island (3020'N, 13030'E), in an effort to reconstruct a high-resolution proxy temperature record over the past two thousand years. In addition, they applied spectral analysis to the δ13C time series in an effort to learn if any significant periodicities were present in the record. The results indicated significant decadal to centennial-scale variability throughout the record, with temperatures fluctuating by about 5C across the series. Most notable among the fluctuations were multi-century warm and cold epochs. Between AD 700-1200, for example, there was about a 1C rise in average temperature (pre-1850 average), which they say "appears to be related to the 'Medieval Warm Period'." In contrast, temperatures were about 2C below the long-term pre-1850 average during the multi-century Little Ice Age that occurred between AD 1580 and 1700. Kitagawa and Matsumoto also report finding significant temperature periodicities of 187, 89, 70, 55 and 44 years. Noting that the 187-year cycle closely corresponds to the well-known Suess cycle of solar activity, and that the 89-year cycle compares well with the Gleissberg solar cycle, they concluded that their findings provide further support for a sun-climate relationship.

Ten years later, Cini Castagnoli et al. (2005) re-examined the Kitagawa and Matsumoto data set for evidence of recurring cycles using Singular Spectrum Analysis and Wavelet Transform, after which it was compared with a 300-year record of sunspots. Results of the newer analyses showed a common 11-year oscillation in phase with the Schwabe cycle of solar activity, plus a second multi-decadal oscillation (of about 87 years for the tree-ring series) in phase with the amplitude modulation of the sunspot number series over the last 300 years, which led this second group of scientists to conclude that the overall phase agreement between the climate reconstruction and variation in the sunspot number series "favors the hypothesis that the [multi-decadal] oscillation" revealed in the record "is connected to the solar activity."

Turing our attention to China, there have been several studies that have documented a solar influence on temperature from several different proxy temperature indicators. Beginning with stalagmite-derived proxies, Paulsen et al. (2003) utilized high-resolution records of δ13C and δ18O from a stalagmite in Buddha Cave, central China [3340'N, 10905'E], to infer changes in climate there over the last 1270 years. Among the climatic episodes evident in their data were "those corresponding to the Medieval Warm Period, Little Ice Age and 20th-century warming, lending support to the global extent of these events." The data also revealed a number of other cycles superimposed on these major millennial-scale temperature cycles, which they attributed to cyclical solar and lunar phenomena.

In a separate study, Tan et al. (2004) established an annual layer thickness chronology for a stalagmite from Beijing Shihua Cave and reconstructed a 2650-year (BC 665-AD 1985) warm season (MJJA: May, June, July, August) temperature record for Beijing by calibrating the thickness chronology with the observed MJJA temperature record (Tan et al., 2003). Results of the analysis showed that the warm season temperature record was "consistent with oscillations in total solar irradiance inferred from cosmogenic 10Be and 14C," and that it also "is remarkably consistent with Northern Atlantic drift ice cycles that were identified to be controlled by the sun through the entire Holocene [Bond et al., 2001]." Going backwards in time, both records clearly depict the start of the Modern Warm Period, the prior Little Ice Age, the Medieval Warm Period, the Dark Ages Cold Period, the Roman Warm Period, and the cold climate at the start of both records.

The researchers concluded that "the synchronism between the two independent sun-linked climate records therefore suggests that the sun may directly couple hemispherical climate changes on centennial to millennial scales." It also stands to reason that the cyclical nature of the millennial-scale oscillation of climate that is evident in both climate records further suggests there is no need to invoke rising atmospheric CO2 concentrations as a cause of the development of the Current Warm Period.

Working with a stalagmite found in still another Chinese cave, Wanxiang Cave (3319'N, 10500'E), Zhang et al. (2008) developed a δ18O record with an average resolution of 2.5 years covering the period AD 190 to 2003. According to the seventeen authors of this study, the δ18O record "exhibits a series of centennial to multi-centennial fluctuations broadly similar to those documented in Northern Hemisphere temperature reconstructions, including the Current Warm Period, Little Ice Age, Medieval Warm Period and Dark Age Cold Period."

In addition, Zhang et al. state that their δ18O record "correlates with solar variability, Northern Hemisphere and Chinese temperature, Alpine glacial retreat, and Chinese cultural changes." And since none of the last four phenomena can influence the first one, it stands to reason that solar variability is what has driven the variations in every other factor mentioned. In fact, in a commentary that accompanied Zhang et al.'s article, Kerr (2008) states that the Zhang et al. record is described by other researchers as "amazing," "fabulous," and "phenomenal," and that it "provides the strongest evidence yet for a link among sun, climate, and culture."

Still in China, we turn next to the study of Hong et al. (2000), who developed a 6000-year high-resolution δ18O record from plant cellulose deposited in a peat bog in the Jilin Province of China (42 20' N, 126 22' E) from which they inferred the temperature history of that location over the past six millennia. They then compared this record with a previously-derived δ14C tree-ring record that is representative of the intensity of solar activity over this period.

Results indicated the study area was relatively cold between 4000 and 2600 BC. Then it warmed fairly continuously until it reached the maximum warmth of the record about 1600 BC, after which it fluctuated about this warm mean for approximately 2000 years. Starting about AD 350, however, the climate began to cool, with the most dramatic cold associated with three temperature minima centered at about AD 1550, 1650 and 1750, corresponding to the most severe cold of the Little Ice Age.

Of particular note is the researchers' finding of "an obvious warm period represented by the high δ18O from around AD 1100 to 1200 which may correspond to the Medieval Warm Epoch of Europe." They also report that "at that time, the northern boundary of the cultivation of citrus tree (Citrus reticulata Blanco) and Boehmeria nivea (a perennial herb), both subtropical and thermophilous plants, moved gradually into the northern part of China, and it has been estimated that the annual mean temperature was 0.9-1.0C higher than at present."

Last of all, Hong et al. say "there is a remarkable, nearly one to one, correspondence between the changes of atmospheric δ14C and the variation in δ18O of the peat cellulose," which led them to conclude that the temperature history of the past 6000 years at the site of their study was "forced mainly by solar variability."

In another study, eighteen radiocarbon-dated aeolian and paleosol profiles within a 1500-km-long belt along the arid to semi-arid transition zone of north-central China were analyzed by Porter and Weijian (2006) to determine variations in the extent and strength of the East Asian summer monsoon throughout the Holocene.

The dated paleosols and peat layers, in the words of Porter and Weijian, "represent intervals when the zone was dominated by a mild, moist summer monsoon climate that favored pedogenesis and peat accumulation," while "brief intervals of enhanced aeolian activity that resulted in the deposition of loess and aeolian sand were times when strengthened winter monsoon conditions produced a colder, drier climate." They also report that the climatic variations they discovered "correlate closely with variations in North Atlantic drift-ice tracers that represent episodic advection of drift ice and cold polar surface water southward and eastward into warmer subpolar water."

The researchers state that "the correspondence of these records over the full span of Holocene time implies a close relationship between North Atlantic climate and the monsoon climate of central China." They also state that the most recent of the episodic cold periods, which they identify as the Little Ice Age, began about AD 1370, while the preceding cold period ended somewhere in the vicinity of AD 810. Consequently, their work implies the existence of a medieval warm period that began some time after AD 810 and ended some time before AD 1370. In addition, their relating of this millennial-scale climate cycle to the similar-scale drift-ice cycle of Bond et al. (2001) implies they accept solar forcing as the most likely cause of the alternating multi-century mild/moist and cold/dry periods of North-Central China. As a result, Porter and Weijian's work helps to establish the global extent of the Medieval Warm Period, as well as its likely solar origin.

Much more evidence of a solar climate link has been obtained from the Tibetan Plateau in China. Wang et al. (2002), for example, studied changes in δ18O and NO3- in an ice core retrieved from the Guliya Ice Cap (3517'N, 8129'E) there, comparing the results they obtained with ancillary data from Greenland and Antarctica. Two cold events -- a weak one around 9.6-9.2 thousand years ago (ka) and a strong one universally referred to as the "8.2 ka cold event" -- were identified in the Guliya ice core record. The researchers report that these events occurred "nearly simultaneously with two ice-rafted episodes in the North Atlantic Ocean," and they add that both events occurred during periods of weakened solar activity.

Remarking that evidence for the 8.2 ka cold event "occurs in glacial and lacustrine deposits from different areas," the authors say this evidence "suggests that the influence of this cold event may have been global." They also say that "comprehensive analyses indicate that the weakening of solar insolation might have been the external cause of the '8.2 ka cold event'," and that "the cause of the cold event around 9.6-9.2 ka was also possibly related to the weaker solar activity." Hence, they conclude that all of these things considered together imply that "millennial-scale climatic cyclicity might exist in the Tibetan Plateau as well as in the North Atlantic."

In a contemporaneous paper enlarging this thesis, Xu et al. (2002) studied plant cellulose δ18O variations in cores retrieved from peat deposits west of Hongyuan County at the northeastern edge of the Qinghai-Tibetan Plateau (32 46'N, 102 30'E). Based on their analysis, they report finding the existence of three consistently cold events that were centered at approximately 500, 700 and 900 AD, during what is sometimes referred to as the Dark Ages Cold Period. Then, from AD 1100-1300, they report that "the δ18O of Hongyuan peat cellulose increased, consistent with that of Jinchuan peat cellulose and corresponding to the 'Medieval Warm Period'." Finally, they note that "the periods 1370-1400 AD, 1550-1610 AD, [and] 1780-1880 AD recorded three cold events, corresponding to the 'Little Ice Age'."

Regarding the origins of these climatic fluctuations, power spectrum analyses of the data revealed periodicities of 79, 88 and 123-127 years, "suggesting," in their word, "that the main driving force of Hongyuan climate change is from solar activities." In a subsequent paper by the same scientists four years later, Xu et al. (2006) compared the Hongyuan temperature variations with solar activity inferred from atmospheric 14C and 10Be concentrations measured in a South Pole ice core, after which they performed cross-spectral analyses to determine the relationship between temperature and solar variability, comparing their results with similar results obtained by other researchers around the world. So what did they learn this time?

Xu et al. (2006) report that "during the past 6000 years, temperature variations in China exhibit high synchrony among different regions, and importantly, are in-phase with those discovered in other regions in the northern hemisphere." They also say that their "comparisons between temperature variations and solar activities indicate that both temperature trends on centennial/millennial timescales and climatic events are related to solar variability."

The researchers' final conclusion was that "quasi-100-year fluctuations of solar activity may be the primary driving force of temperature during the past 6000 years in China." And since their data indicate that peak Medieval Warm Period temperatures were higher than those of the recent past, it is not unreasonable to assume that the planet's recent warmth may have been solar-induced as well.

Still in the northeast edge of the Tibetan Plateau, two years later Tan et al. (2008) developed a precipitation history of the Longxi area of the plateau's northeast margin since AD 960 based on an analysis of Chinese historical records, after which they compared the result with the same-period Northern Hemisphere temperature record and contemporaneous atmospheric 14C and 10Be histories. This work revealed, in their words, that "high precipitation of Longxi corresponds to high temperature of the Northern Hemisphere, and low precipitation of Longxi corresponds to low temperature of the Northern Hemisphere." Consequently, their precipitation record may be used to infer a Medieval Warm Period that stretched from approximately AD 960 to 1230, with temperature peaks in the vicinity of AD 1000 and 1215 that clearly exceeded the 20th-century peak temperature of the Current Warm Period. They also found "good coherences among the precipitation variations of Longxi and variations of atmospheric 14C concentration, the averaged 10Be record and the reconstructed solar modulation record," which findings harmonize, as they describe it, with "numerous studies [that] show that solar activity is the main force that drives regional climate changes in the Holocene," in support of which statement they attach 22 other scientific references. The researchers' ultimate conclusion, therefore was that the "synchronous variations between Longxi precipitation and Northern Hemisphere temperature may be ascribed to solar activity, " which apparently produced a Medieval Warm Period that was both longer and stronger than what has been experienced to date during the Current Warm Period in the northeast margin of the Tibetan Plateau.

Lastly, Xu et al. (2008) studied decadal-scale temperature variations of the past six centuries derived from four high-resolution temperature indicators -- the δ18O and δ13C of bulk carbonate, total carbonate content, and the detrended δ15N of organic matter -- which they extracted from Lake Qinghai (3632'-3715'N, 9936'-10047'E) on the northeast Qinghai-Tibet plateau, comparing the resultant variations with proxy temperature indices derived from nearby tree rings and reconstructed solar activity. Results of the analysis showed "there are four obvious cold intervals during the past 600 years at Lake Qinghai, namely 1430-1470, 1650-1715, 1770-1820 and 1920-1940," and that "these obvious cold intervals are also synchronous with the minimums of the sunspot numbers during the past 600 years," namely, "the Sporer, the Maunder, and the Dalton minimums," which facts strongly suggest, in their words, "that solar activities may dominate temperature variations on decadal scales at the northeastern Qinghai-Tibet plateau."

In concluding this summary, we note that If the development of the significant cold of the worldwide Little Ice Age was driven by a concomitant change in some type of solar activity (which seems fairly well proven by a wealth of real-world data, of which several of the studies described above are examples), it logically follows that the "undevelopment" of the Little Ice Age (i.e., the global warming of the 20th century) was primarily driven by the reversal of that change in solar activity, and not by the historical rise in the air's CO2 content.

References
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Last updated 29 July 2009